Digital camera and control method thereof

ABSTRACT

A digital camera including a lens, first and second sensors, a shutoff member, a display, a detector, an exposure amount determiner, and a still image generator. The first sensor receives light through the lens and the second sensor also receives light through the lens, but is different from the first sensor. The shutoff member performs a first shutoff of the light received by the first sensor through the lens and also ends the first shutoff. The display displays a moving image based on the light received by the first sensor, and while the moving image is displayed, the detector detects a shutter operation. The exposure amount determiner determines, in response to the detected shutter operation, an exposure amount based on the light received by the second sensor when the first sensor does not receive light through the lens. The still image generator generates a still image based on the light received by the first sensor and the exposure amount determined by the exposure amount determiner.

BACKGROUND OF THE INVENTION

The present invention relates to a digital camera and a control methodthereof, and more specifically, to a digital camera using a shuttercurtain which operates mechanically and using an area image sensor whichdoes not have a structure for a high-speed draft mode, and a controlmethod thereof.

A CCD area image sensor which divides electric charges stored inphotodiodes into charges of a plurality of divided fields to transferthem is known (refer to, for example, JP-A-8-18875 and Japanese PatentNo. 3009041). By dividing electric charges stored in photodiodes intocharges of a plurality of divided fields to transfer them, the area ofthe vertical CCD can be reduced. As a result, since the area of thephotodiodes can be increased, this becomes advantageous from theviewpoint of the saturated amount of signals. A digital camera providedwith an electronic viewfinder is often mounted with an area image sensorcorresponding to a high-speed draft mode, with a function of selectivelyreading charges at regular intervals from a plurality of photodiodes,which are arrayed along the vertical CCD, in order to increase the framerate of a moving image which is displayed in real time on the electronicviewfinder. Since the area image sensor corresponding to a high-speeddraft mode is provided with a dedicated control signal line for readingthe charges stored in the photodiodes at one time by thinning out themaccording to a rule capable of forming a color image, pixels in avertical direction from all pixels can be thinned out and read out. As aresult, since a grainy image representing a whole image, that is, animage having a low resolution can be read, the frame rate of a movingimage can be increased by reading the grainy image in a short time.

However, since a digital camera provided with a high-resolution CCDimage sensor which is not corresponding to the high-speed draft modecannot increase the frame rate of a moving image, it has a difficulty inrealizing a moving image display function by the electronic viewfinder.In a digital camera provided with a high-sensitivity and high-resolutionCCD image sensor, exposure is often by a shutter curtain which operatesmechanically.

SUMMARY

It is therefore an object of the invention to provide a digital cameraand its control method capable of controlling exposure of a still imageby a shutter curtain which operates mechanically to display a movingimage in real time and capable of increasing the frame rate of a movingimage, even if an area image sensor does not have a structure for ahigh-speed draft mode.

In order to achieve the object, according to the invention, there isprovided a control method of a digital camera comprising:

displaying a moving image on a screen based on charges stored in animage sensor by an electronic shutter with a shutter curtain opened;

detecting illuminance of the shutter curtain with the shutter curtainclosed;

setting a still image exposure period based on the detected illuminanceof the shutter curtain;

exposing the image sensor in the still image exposure period with theshutter curtain opened; and

storing a still image in a recording medium based on the charges storedin the image sensor in the still image exposure period.

With this configuration, by storing the charges in the image sensor bythe electronic shutter with the shutter curtain opened, the moving imagecan be displayed in real time on the screen on the basis of the chargesstored in the image sensor. By setting the still image exposure periodon the basis of the detected illuminance of the shutter curtain in itsclosed state, and opening the shutter curtain in the still imageexposure period, exposure of a still image can be controlled by themechanical shutter curtain.

The displaying process may include: storing the charges in photodiodesof the image sensor; transferring the charges, which belong to aplurality of fields being different from each other and constituting oneframe, from the photodiodes to a vertical element of the image sensor intime-division manner; transferring the charges in every field from thevertical element to a horizontal element of the image sensor;transferring the charges in every field from the horizontal element to adetecting element of the image sensor; generating pixel signalscorresponding to the charges transferred to the detecting element inevery field; and generating a plurality of continuous frames based oneach pixel signal while displaying each frame as the moving image.

In this case, by using the pixel signals of one field for generation ofpixel signals of a plurality of continuous frames, and by overlappingthe pixel signals of one field with a plurality of frames, even if theimage sensor does not have a structure for a high-speed draft mode, theframe rate of the moving image of a digital camera can be increased.

The charges in a plurality of cells of the vertical element may betransferred to and accumulated in each of cells of the horizontalelement.

In this case, by accumulating the charges for a plurality of cells ofthe vertical element in each cell of the horizontal element andtransferring charges of each cell of the horizontal element to thedetecting element, the number of times of transfer of charges by thevertical element can be reduced. As a result, the frame rate of a movingrate of a digital camera can be increased.

The displaying process may include: storing the charges in photodiodesof the image sensor; transferring the charges, which belong to aplurality of fields being different from each other and constituting oneframe, from the photodiodes to a vertical element of the image sensor intime-division manner; transferring the charges in every field from thevertical element to a horizontal element of the image sensor;transferring the charges in every field from the horizontal element to adetecting element of the image sensor; generating pixel signalscorresponding to the charges transferred to the detecting element inevery field; and generating each frame based on each pixel signal whiledisplaying each frame as the moving image.

In this case, a frame of a monotone image can be generated on the basisof the charges of photodiodes corresponding to some color components ofall the color components. Accordingly, even if a digital camera is notprovided with dedicated signal lines for a high-speed draft mode, theframe rate can be increased by transmitting, to control signal lines fordetecting time-divided charges of photodiodes in every field, controlsignals for detecting charges of the photodiodes for one field in everyframe, and displaying each frame of a monotone moving image on thescreen on the basis of the charges of the photodiodes for one field.

The charges in a plurality of cells of the vertical element may betransferred to and accumulated in each of cells of the horizontalelement.

In order to achieve the object, according to the invention, there isalso provided a digital camera comprising:

an image sensor;

a shutter curtain, adapted to expose and shield the image sensor;

a display controller, operable to display a moving image on a screenbased on charges stored in the image sensor by an electronic shutterwith the shutter curtain opened; and

a still image recorder, operable

-   -   to detect illuminance of the shutter curtain with the shutter        curtain closed,    -   to set a still image exposure period based on the illuminance,    -   to expose the image sensor in the still image exposure period        with the shutter curtain opened, and    -   to store a still image in a recording medium based on the        charges stored in the image sensor in the still image exposure        period.

The image sensor may include a first controller, operable: to store thecharges in photodiodes of the image sensor; to transfer the charges,which belong to a plurality of fields being different from each otherand constituting one frame, from the photodiodes to a vertical elementof the image sensor in time-division manner; to transfer the charges inevery field from the vertical element to a horizontal element of theimage sensor; and to transfer the charges in every field from thehorizontal element to a detecting element of the image sensor. Thedisplay controller may include a second controller, operable: togenerate pixel signals corresponding to the charges transferred to thedetecting element in every field; to generate a plurality of continuousframes based on each pixel signal; and to display each frame as themoving image.

The charges in a plurality of cells of the vertical element may betransferred to and accumulated in each of cells of the horizontalelement.

The image sensor may include a first controller, operable: to store thecharges in photodiodes of the image sensor; to transfer the charges,which belong to a plurality of fields being different from each otherand constituting one frame, from the photodiodes to a vertical elementof the image sensor in time-division manner; to transfer the charges inevery field from the vertical element to a horizontal element of theimage sensor; and to transfer the charges in every field from thehorizontal element to a detecting element of the image sensor. Thedisplay controller may include a second controller, operable: togenerate pixel signals corresponding to the charges transferred to thedetecting element in every field; to generate each frame based on eachpixel signal; and to display each frame as the moving image.

The charges in a plurality of cells of the vertical element aretransferred to and accumulated in each of cells of the horizontalelement.

In addition, the order of respective operations of the method as setforth in claims is not limited to the described order unless there aretechnical impediments. For example, the operations may be executed in anarbitrary order or may be executed at the same time. Further, therespective functions of a plurality of units installed in the presentinvention are implemented by hardware resources whose functions arespecified by their own construction, software resources whose functionsare specified by programs, or combinations of the hardware and softwareresources. Further, the respective functions of the plurality of unitsare not limited to those which are implemented by software resourcesphysically independent from each other. Further, the present inventioncan be specified not only as an invention of a program but also as aninvention of a recording medium in which the program is recorded.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1C are views showing the appearance of a digital stillcamera according to a first embodiment.

FIGS. 2A and 2B are views showing the appearance of the digital stillcamera according to the first embodiment.

FIG. 3 is a block diagram of the digital still camera according to thefirst embodiment.

FIG. 4 is a schematic view of an image sensor related to the firstembodiment.

FIGS. 5A and 5B are schematic views for explaining a read method of theimage sensor related to the first embodiment.

FIG. 6 is a flowchart showing the flow of processing in a photographingmode related to the first embodiment.

FIGS. 7A to 7D are schematic views showing the operation of the imagesensor related to the first embodiment.

FIG. 8 is a schematic view showing driving signals of the image sensorrelated to the first embodiment.

FIG. 9 is a schematic view for explaining the processing which generatesframe data from pixel signals.

FIG. 10 is a schematic view for explaining the processing whichgenerates frame data from pixel signals.

FIG. 11 is a flowchart showing the operation of the image sensor in thethrough image display processing.

FIG. 12 is a schematic view of a digital still camera according to asecond embodiment.

FIG. 13 is a flowchart showing the flow of processing in a photographingmode related to the second embodiment.

DETAIL DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, a plurality of embodiments of the invention will bedescribed with reference to the accompanying drawings. The components ofeach embodiment to which the same reference numerals are givencorrespond to those of other embodiments to which the reference numeralsare given.

First Embodiment

FIGS. 1A, 1B, 1C and 2A are views showing the appearance of a digitalstill camera (DSC) 1 according to a first embodiment of the invention.FIG. 2B is a view showing that a replaceable lens unit 2 is mounted tothe DSC 1. FIG. 3 is a block diagram showing the DSC 1.

In addition, although the DSC 1 is of a compact camera type, it may beof a single lens reflex camera type.

In the DSC 1, a plurality of kinds of replaceable lens units 2 can bemounted to a mount 28. A focus adjusting dial 58 and a diaphragmadjusting dial 56 are provided outside a lens barrel of each lens unit2. When the focus adjusting dial 58 rotates, lenses 60 and 64 move inthe direction of an optical axis. A focus can be adjusted by rotatingthe focus adjusting dial 58. When the diaphragm adjusting dial 56rotates, the aperture of a diaphragm 62 varies. The diaphragm can beadjusted by rotating the diaphragm adjusting dial 56.

A first shutter curtain 30 and a second shutter curtain 32 constitute anelectrically controlled focal plane shutter. The first shutter curtain30 and the second shutter curtain 32 are put into an operable state byrotating a winding lever 14, and their mechanical opening and shutoffoperations are electrically controlled by a shutter driving part 70.That is, when the shutter starts to operate, the first shutter curtain30 operates first, and shutoff of the light projected through the lenseswithin the replaceable lens unit 2 is opened. Therefore, exposure of theimage sensor 72 starts, and this exposure is continued during the perioduntil the second shutter curtain 32 operates. Then, since the lightprojected through the lenses with the completion of the operation of thesecond shutter curtain 32 is shut off again, the exposure is completed.

In addition, the construction of the shutter is not limitedparticularly. For example, the shutter may be a shutter in whichelectric control is not used for operation of a shutter curtain or maybe a shutter in which the charge storage time of the image sensor 72 iscontrolled by a so-called electronic shutter which controls a substratevoltage, without using the shutter curtain.

The internal illuminance meter 66 is an optical sensor which measuresthe illuminance of the reflected light of the shutter curtain. Theilluminance of the light which is incident on the internal illuminancemeter 66 varies according to the aperture of the diaphragm 62.Therefore, if the diaphragm adjusting dial 56 rotates, the output valueof the internal illuminance meter 66 also varies. The quantity of thelight projected through the lenses within the replaceable lens unit 2can be measured according to the output of the internal illuminancemeter 66 which measures the illuminance of the reflected light of theshutter curtain. The result of this measurement is used for calculationof shutter speed, that is, an exposure period or the like of the imagesensor 72 by the DSC 1.

It is noted herein that the surface of the shutter curtain in aphotographing preparatory state is not painted in plain deep black orpure white, but is painted so that its refractive index becomes about18%. As a result, the illuminance of the light projected through thelens unit 2 can be more exactly measured by the internal illuminancemeter 66. Further, if the intense reflected light is incident on theshutter curtain, the internal illuminance meter 66 cannot measure theilluminance of the reflected light exactly. In this case, since a properexposure period cannot be calculated, photographing with proper exposurecannot be performed. Thus, by forming rough minute satin on the surfaceof the shutter curtain, the light incident on the shutter curtain isgently diffused on the surface of the shutter curtain. As a result,since the light gently diffused on the surface of the shutter curtain isincident on the internal illuminance meter 66, the illuminance of thelight incident on the internal illuminance meter 62 can be measuredexactly. Further, as for the photographing of the DSC 1, the refractiveindex of a central portion of the shutter curtain is made different fromthat of a peripheral portion thereof so that centralized exposurephotographing becomes possible. Specifically, the reflecting quantity ofthe shutter curtain is adjusted by, for example, painting the shuttercurtain in deeper color toward the peripheral portion so that therefractive index of the surface of the shutter curtain is reduced fromthe central portion of the shutter curtain toward the peripheral portionthereof. Further, the internal illuminance meter 62 is adjusted tooutput exact illuminance if the reflective index of the lens unit 2 inits optical path direction by the shutter curtain becomes about 18%.

In addition, in a construction which does not use a shutter curtain, theimage sensor 72 can directly detect the illuminance of the light passedthrough the lens unit 2 or the internal illuminance meter 66 canindirectly detect the reflected light of a half mirror.

FIG. 4 is a schematic view of the image sensor 72. FIGS. 5A and 5B areschematic views for explaining a reading method of the image sensor 72.

The image sensor 72 is a so-called CCD color area image sensor composedof photodiodes 720, vertical CCDs 721, a horizontal CCD 722, a detectingelement 723, etc., which are discretely arranged in a two-dimensionalspace. The image sensor 72 includes R, G, and B color filters which areBayer-arrayed in every photodiode 720, and stores in each photodiode 720a signal charge showing the density level of any one of RGB channels inevery pixel. In addition, although the image sensor 72 in which thephotodiodes 720 are arrayed in a tetragonal lattice are illustratedherein, the photodiodes 720 of the image sensor 72 may be arrayed in theshape of a honeycomb. Further, the color filters of the image sensors 72may be arrayed in stripes. Further, the image sensor 72 may be a CMOSarea image sensor.

Each vertical CCD 721 has four transfer electrodes which allow avertical driving signal V1, V2, V3, or V4 to be input to every cell 721a. By gradually and sequentially applying vertical driving signals withmutually different phases to the four transfer electrodes, a potentialwell is formed in each cell 721 a of the vertical CCD 721, and anelectric charge bound in the potential well of each cell 721 a moves topotential wells of sequentially adjacent cells 721 a one after another.Signal charges transferred to each cell 721 a from the photodiodes 720in this way are transferred to the horizontal CCD 722. Hereinafter, thetransfer of signal charges by the above-described vertical CCD 721 isreferred to as “vertical CCD transfer.”

The horizontal CCD 722 has two transfer electrodes which allow ahorizontal driving signal Vh1 or Vh2 to be input to every cell 722 a.Different potential wells are formed within the cells 722 a of thehorizontal CCD 722. In addition, by applying the horizontal drivingsignals Vh1 and Vh2 with different phases of 180° to the two horizontaltransfer electrodes, a potential well is formed in every cell 722 a, andan electric charge bound in the potential well of each cell 722 a movesto potential wells of sequentially adjacent cells 722 a one afteranother. Signal charges transferred to each cell 722 a by the verticalCCD 721 in this way are sequentially transferred to the detectingelement 723. Specifically, vertical signal lines 724 and horizontalsignal lines 725 are connected to transfer electrodes (not shown) of thevertical CCD 721 and the horizontal CCD 722, respectively. Also, thevertical CCD 721 and the horizontal CCD 722 are driven by the verticaldriving signals (refer to V1 to V4 in FIG. 8) and the horizontal drivingsignals (refer to Vh1 and Vh2 in FIG. 8), respectively, which areapplied to the above-mentioned signal lines by an image capturingcontroller 76, thereby transferring signal charges.

The detecting element 723 converts charges transferred to the horizontalCCD 722 into pixel signals. Specifically, for example, the detectingelement 723, which is a floating diffusion amplifier, converts signalcharges into voltages values as pixel signals according to itscapacitance. In addition, although the image sensor 72 in which thevertical CCD 721 are of four-phase driving method is illustrated, thevertical CCD 721 may be a CCD of arbitrary phase driving method.Further, although the image sensor 72 in which the horizontal CCD 722 isof two-phase driving method is illustrated, the horizontal CCD 722 ofthe image sensor 72 may be a CCD of arbitrary phase driving method.Further, the detecting element 723 may be a floating gate amplifier.

As shown in FIGS. 5A and 5B, the image sensor 72 is an area image sensorof so-called frame reading method which reads pixel signals of one framewhich are divided into two fields. Since a vertical CCD for reading inthis area image sensor of frame reading method is used for both a firstfield and a second field, the area of the vertical CCD can be reduced.As a result, since the size of the photodiodes 720 can be increased orthe size of the cells 721 a (refer to FIG. 4) of the vertical CCD 721can be increased, it is advantageous in that the area image sensor offrame reading method can increase the saturated amount of signalcharges. The image sensor 72 has a shift electrode for controllingtransfer of signal charges from the photodiodes 720 to a vertical CCD721 between the photodiodes 720 and the vertical CCD 721. A shift signalline 726 and a shift signal line 727 are connected to this shiftelectrode so that, during reading of each field, charge signals showingthe density level of the same channels are transferred to a vertical CCD721 in each column. Specifically, for example, in the image sensor 72having Bayer-arrayed color filters, the shift signal line 726 and theshift signal line 727 are alternately connected to a continuous shiftelectrode. In this case, in the image sensor 72, a signal charge showingthe density level of a G-channel or a B-channel is transferred to thevertical CCD 721 in each column from a photodiode 720 during reading ofthe first field (refer to FIG. 5A), and a signal charge showing thedensity level of an R-channel or a G-channel is transferred to avertical CCD in each column from a photodiode during reading of thesecond field (refer to FIG. 5B).

As such, the image sensor 72 transfers signal charges of mutuallydifferent fields to the vertical CCD 721 in time-division manner to readpixel signals of one frame which is divided into two fields. Inaddition, although the image sensor 72 has been described as the onewhich reads pixel signals of one frame which is divided into two fields,it may be an area image sensor which reads pixel signals of one framewhich are divided into three or more fields. Further, the image sensor72 may be of full pixel reading method, if it has color filters whichare arrayed in stripes.

It is noted herein that the image sensor 72 does not have a structurefor a high-speed draft mode, for example, shift signal lines forselectively transferring signal charges from a plurality of photodiodes720 which are arrayed along a vertical CCD 721. Therefore, in the imagesensor 72, the size of the photodiodes 72 can be further increased, andthe size of the vertical CCD 721 cab be increased. Thus, the saturatedamount of signal charges can be increased. Further, since the area oflight-receiving surfaces of the photodiodes 720 can be increased, thisis advantageous from the viewpoint of sensitivity or the like. However,in the image sensor 72, by thinning out signal charges stored in thephotodiodes 720 to transfer them to the vertical CCD 721 like ahigh-speed draft mode, the number of times of transfer of the signalcharges required to display one frame by the horizontal CCD 722 cannotbe reduced.

For example, if all pixels of an area image sensor of 600 million pixels(3008 pixels in the horizontal direction and 2000 pixels in the verticaldirection) are read at a reading rate of 25 MHz by a related framereading method, a reading time of 0.04 μs per one pixel is required.Therefore, the reading of one field requires a reading time of at least120.32 ms (=0.04 μs×3008×1000). Accordingly, the reading of one framerequires a reading time of 240.64 ms when the reading time for at leasttwo fields is added up. That is, if a continuous image is read anddisplayed using an area image sensor of 600 million pixels which doesnot correspond to the high-speed draft mode (hereinafter referred to as“through image reading”), only four frames can be read for one second.Here, the through image is a series of moving images which are obtainedby photographing a photographic subject at predetermined time intervals.Moreover, this time is purely the time required to read all the pixelsincluding 3008 pixels in the horizontal direction and 2000 pixels in thevertical direction. Generally, since the time to read optical blackpixels arranged around the image sensor 72, the processing time to drivethe image sensor 72, the high-speed emission transfer time for noiseemission, the exposure time of a photographic subject, and the like alsoare required, only two or three frames can be read practically, and thusthe moving posture of a photographic subject cannot be practically readas a moving image.

Therefore, in the DSC 1, an image to be displayed as a moving image doesnot need to have high resolution. Even if it has low resolution, areading method is schemed on the basis of the idea that higher framerate brings a better result. First, after a fixed time of exposure,signal charges for pixels in the first field are shifted to a verticalCCD 721 by a shift signal. Thereafter, transfer of the individual signalcharges in the vertical CCD 721 is carried out. At this time, analogaccumulative addition of signal charges for a plurality of cells in thevertical direction is performed by storing signal charges for aplurality of cells of the vertical CCD 721 in each cell 722 a of thehorizontal CCD 722. In addition, the number of charges to be added upmay be for two cells or for three cells. Then, the signal charges for aplurality of cells of the vertical CCD 721 are transferred by thehorizontal CCD 721.

The number of reading lines of pixel lines in the vertical direction canbe reduced by adding signal charges for a plurality of cells of thevertical CCD 721 as such (for example, if addition for two cells isperformed, the number of reading lines become half, and if addition forfour cells is performed, the number of reading lines becomes onefourth). Therefore, even if a structure for a high-speed draft mode isnot provided, it is possible to reduce the number of transfer of signalcharges by the horizontal CCD 722, which is required to display oneframe of a through image as a moving image. At this time, for example,if addition for two cells and addition for four cells are performed, thenumber of times of transfer of signal charges can be reduced to half andone fourth, respectively, and the frame rate can be increased to twiceand quadruple, respectively. Further, since the apparent sensitivity ofthe image sensor 72 can be raised by adding signal charges, the exposureperiod of the image sensor 72 during display of a through image can beshortened (for example, if addition for two cells are performed, theexposure period is shortened to half, and if addition for four cells isperformed, the exposure period is shortened to one fourth). Accordingly,the frame rate can be further improved. As a result, the DSC 1 candisplay a through image at high speed even if an image sensor 72 with alarge number of pixels, which is capable of photographing a highresolution of a still image. Further, the SN ratio of signal charges canalso be improved by adding signal charges for a plurality of cells ofthe vertical CCD 721. In addition, the moving image may be a movingimage which is recorded by a moving image photographing function of theDSC 1. Further, the number of signal charges to be added may be for twocells, for three cells, or for four cells, or may be changedautomatically or manually. Hereinafter, “adding signal charges for ‘n’cells of the vertical CCD 721 in each column to each of the cells 722 aof the horizontal CCD 722” is referred to “n-time pixel addition.”

The image capturing controller 76 shown in FIG. 3 applies verticaldriving signals, horizontal driving signals, and shift signals to thetransfer electrodes of the vertical CCD 721, the transfer electrodes ofthe horizontal CCD 722, and the shift electrode, respectively, via thevertical signal lines 724, the horizontal signal lines 725, and theshift signal lines 726 and 727, respectively.

An analog front end (AFE) 74 is composed of a correlation doublesampling (CDS) circuit 740, an amplifier 742, an analog/digital (ND)converter 744, an analog black level reproducing circuit (a circuitwhich reproduces a reference voltage of optical black by settling thesignal level of black by using pixels, which are optically masked, inthe image sensor 72) which is not shown, etc. The CDS circuit 740 is acircuit which removes reset noises concluded in pixel signals output bythe image sensor 72. The amplifier 742 is an amplifier, i.e., aso-called variable gain amplifier to amplify pixel signals with gainscorresponding to the brightness of a photographic subject. The A/Dconverter 744 generates digital pixel signals (hereinafter referred toas pixel data) by performing ND conversion on pixel signals. The pixeldata output from the AFE 74 is stored in a RAM 100 by an imageprocessing controller 98.

The image processing controller 98 performs a variety of imageprocessing on the image data output from the AFE 74, in cooperation withthe RAM 100, a color processing part 102, a resolution converting part104, and an image compression/extension part 106.

The RAM 100 is a volatile memory in which pixel data, etc. aretemporarily stored.

The color processing part 102 cooperates with the image processingcontroller 98, and performs image development processing on the pixeldata output from the AFE 74. The development processing is processingwhich generates frame data having density levels of three RGB channelsin every pixel by means of white balance correction, gradationcorrection, and demosaic processing which interpolates the density levelof each pixel of pixel data corresponding to a signal charge of eachphotodiode 720 on the image sensor 72 between neighboring pixels, andwhich finally reproduces the frame data in the form of an image.

The resolution converting part 104 cooperates with the image processingcontroller 98, and converts the resolution (total number of pixels) offrame data to a predetermined resolution. Specifically, for example, theresolution converting part 104 converts the resolution of frame data toa resolution corresponding to the photographing conditions set by a userbefore photographing, or converts the resolution of frame data to aresolution corresponding to the screen size of an LCD 36.

The compression/extension part 106 cooperates with the image processingcontroller 98, and compresses frame data and extends compressed framedata (for example, the compression/extension part compresses image datainto image data of the JPEG format or extends data compressed into theJPEG format). In addition, the compression/extension part can also storeframe data in the removable memory 92 without compressing the framedata.

A graphic controller 94 cooperates with the image processing controller98, and displays an image represented by frame data on the screen of theLCD 36.

The above-described functions of the image processing controller 98, thecolor processing part 102, the resolution converting part 104, thecompression/extension part 106, and the graphic controller 94 may beimplemented by dedicated circuits, such ASIC and DSP, or may beimplemented by execution of a specific program of a control section 80.

The operating part 84 has a power switch 52, a release button 10, ashutter speed dial 12, buttons 40, 42, 44, 46, 48 and 50 for settingphotographing conditions, and a jog dial 22.

An external interface controller 86 communicably connects the DSC 1 withexternal systems, such as a personal computer (PC) (not shown). Aremovable memory controller 88 is an input/output mechanism whichtransfers the data stored in the RAM 100 to the removable memory 92 as arecording medium connected to a card connector 90. In addition, therecording medium may be built-in memories, such as a flash memory 82.

The flash memory 82 is a volatile memory which stores image processingprograms to be executed by the control section 80. Image processingprograms and various kinds of data which are necessary for operation ofthe DSC 1 can also be stored in the flash memory 82 by downloading overnetworks from a predetermined server, reading from the removable memory92, or the like.

The control section 80 has a CPU 78, a RAM 81, and a flash memory 82.The control section 80 executes the control programs stored in the flashmemory 82 to control respective parts of the DSC 1, and also functionsas a display control unit and a still image recording unit. The RAM 81is a volatile memory which temporarily stores control programs andvarious kinds of data.

FIG. 6 is a flowchart showing the flow of processing in a through imagephotographing mode of the DSC 1. The processing shown in FIG. 6 isstarted when the DSC 1 transits to the through image photographing mode,and the processing is repeated until the DSC 1 transits from the throughimage photographing mode to any mode other than the through imagephotographing mode.

First, the control section 80 opens the first shutter curtain 30 and thesecond shutter curtain 32 in cooperation with the shutter driving part70 (refer to Step S100). Hereinafter, the expression “open the firstshutter curtain 30 and the second shutter curtain 32” is referred to as“open the shutter curtain.”

In Step S102, the control section 80 displays a through image on thescreen of the LCD 36. Specifically, the control section 80 makes signalcharges stored in the photodiodes 720 for a predetermined period ofexposure using an electronic shutter with the shutter curtain opened,and reads pixel signals according to these signal charges from the imagesensor 72. Then, the control section 80 generates frame data from theread pixel signals, and performs pixel interpolation procession for eachof R, G and B, white balancing processing, color reproductionprocessing, gamma correction processing, andvertical-and-horizontal-size reducing processing, etc. on this framedata, thereby displaying an image for one frame represented by the framedata after the various kinds of processing. The control section 80repeats the series of processing to display a through image as a movingimage on the LCD 36. The detailed description thereof will be madebelow.

In Step S104, the control section 80 determines whether or not therelease button 10 has been pushed. If the release button 10 is pushed,the control section 80 executes processing (refer to Step S106 to StepS118) for photographing a still image of a photographic subject.

In Step S106, the control section 80 closes the first shutter curtain 30and the second shutter curtain 32 in cooperation with the shutterdriving part 70 (hereinafter referred to as “close the shuttercurtain”), and then performs charge of the shutter for the next shutteroperation, preparation of the image sensor 72 for the nextphotographing, etc.

In Step S108, the control section 80 detects the illuminance of curtainsurface reflected light reflected by the first shutter curtain 30 or thesecond shutter curtain 32. Specifically, the control section 80 readsoutput signals of the internal illuminance meter 66, thereby detectingthe illuminance of the light which is transmitted through the diaphragm62 of the lens unit 2 and reflected by the shutter curtain.

In Step S110, the control section 80 sets an optimal exposure period (aproper period in which the shutter curtain is to be opened) underphotographing conditions according to the illuminance of the curtainsurface reflected light. Specifically, the control section 80 sets anexposure period on the basis of output signals of the internalilluminance meter 66.

In Step S112 to Step S114, the control section 80 opens the shuttercurtain only for the exposure period set in Step S110. Specifically, thecontrol section 80 performs preparation for exposure of the image sensor72 prior to the opening of the shutter curtain (for example, emissionprocessing of charges stored in the individual photodiodes 720 of theimage sensor 72 and emission processing of charges remaining in thevertical CCDs 721 and the horizontal CCD 722). Then, if preparation forthe exposure of the image sensor 72 is made, the control section 70opens the shutter curtain in cooperation with the shutter driving part70 (refer to Step S112), and closes the shutter curtain after the setexposure period has elapsed from when the shutter curtain has beenopened (refer to Step S114). As a result, the image sensor 72 is exposedto the light from a photographic subject only for the exposure period.

In Step S116 to Step S118, the control section 80 generates a stillimage. Specifically, the control section 80 makes the charges remainingin the vertical CCDs 721 and the horizontal CCD 722 of the image sensor72 emitted, and thereafter reads pixel signals of a first field andpixel signals of a second field sequentially from the image sensor 72(refer to Step S116). Then, the control section 80 performs developmentprocessing on the read pixel signals of the first field and the readpixel signals of the second field in cooperation with the colorprocessing part 102, thereby generating frame data from the pixelsignals of the first field and the pixel signals of the second field.Moreover, the control section 80 performs resolution conversionprocessing, compression processing (for example, compressing processingaccording to the JPEG standard), and the like on the frame data, incooperation with the resolution conversion part 104, thecompression/extension part 106, the image processing controller 98, andthe removable memory controller 88, and stores the frame data in theremovable memory 92, etc. (refer to Step S118) as a still image (forexample, a still image of the JPEG format).

FIGS. 7A to 7D are schematic views showing the operation of the imagesensor 72 in the through image display processing. FIG. 8 is a schematicview showing driving signals output by the image capturing controller 76in the through image display processing. FIGS. 7A to 7D respectivelyshow states of the image sensor 72 at t1 to t4 of FIG. 8. FIG. 9 is aschematic view showing the processing which generates frame data frompixel signals in the through image display processing. Hereinafter, thethrough image processing will be described while the processing whichreads pixel signals of a first field from the image sensor 72, andgenerates frame data for one frame from the read pixel data of the firstfield, and its previously read pixel signals of the second field isspecifically described.

First, the control section 80 transfers signal charges of a first fieldto the individual cells 721 a of the vertical CCD 721 from thephotodiodes 720 (refer to waveforms of Vsh at t1 shown in FIG. 7A andFIG. 8). At this time, signal charges showing the density level of thesame channels, specifically, signal charges showing the density level ofG channels, or signal charges showing the density level of B channelsare transferred to all the cells 721 a of the vertical CCD 721 in eachcolumn from the corresponding photodiodes 721.

Next, the control section 80 adds up signal charges for a plurality ofcells of the vertical CCD 721 in each column, in each cell 722 a of thehorizontal CCD 722. Specifically, for example, when signal charges fortwo cells of the vertical CCD 721 in each column are added up, thecontrol section 80 makes the vertical CCD 721 transfer signal chargesfor two cells of the vertical CCD 721 to each cell 722 a of thehorizontal CCD 722, without driving the horizontal CCD 722 (refer towaveforms of Vh at t1 to t5 shown in FIG. 8). Waveforms V1 to V4 at t1to t3 shown in FIGS. 7B and 7C and FIG. 8 show vertical driving signalsfor transferring a signal charge in the first cell, and Waveforms V1 toV4 at t4 to t5 shown in FIG. 7D and FIG. 8 show vertical driving signalsfor transferring a signal charge in the second cell. As a result, signalcharges for two cells of the vertical CCD 721 in each column are storedin each cell 722 a of the horizontal CCD 722. In addition, signalcharges showing the density level of the same channels are transferredto the vertical CCD 721 in each column as described above, signalcharges showing the density level of different channels are not mixed ineach cell 722 a of the horizontal CCD 722 by the pixel addition.However, even if signal charges showing the density level of mutuallydifferent channels are mixed in the pixel addition, generation of amonotone through image is possible. Therefore, signal charges showingthe density level of different channels may be transferred to thevertical CCD 721 in each column. However, even if signal charges showingthe density level of mutually different channels are mixed in the pixeladdition, for example, a monotone through image is displayed, signalcharges showing the density level of different channels may betransferred to the vertical CCD 721 in each column.

Next, the control section 80 makes the horizontal CCD 722 transfer thesignal charges after the pixel addition to the detecting element 723(refer to waveforms of Vh at t5 to t6 shown in FIG. 8), and makes thedetecting element 723 convert the signal charges into pixel signals.That is, the horizontal CCD 722 clears off charges only once whenevercharges for two cells of a vertical CCD are stored in each cell. In theDSC 1, the number of times of transfer of signal charges of thehorizontal CCD 722 can be reduced in this manner, thereby reducing thenumber of times of transfer of signal charges by the vertical CCD 721,which is required for displaying one frame. Specifically, the number oftimes of transfer by the vertical CCD 721, which is required fordisplaying one frame is reduced to one n-th by n-time pixel addition. Asa result, pixel signals required for displaying one frame can be outputat high speed from the image sensor 72. In addition, when the detectingelement 723 is a floating diffusion amplifier, the control section 80may transfer signal charges for a plurality of cells of the vertical CCD722 to the detecting element 723, thereby making the detecting element723 convert signal charges into pixel signals after addition of thesignal charges by the detecting element 723.

Noise removal by the AFE 74, brightness adjustment, ND conversion, etc.are performed on the pixel signals read from the image sensor 72.Specifically, the brightness adjustment is performed when the controlsection 80 controls the gain of the amplifier 742 according to thebrightness of a photographic subject. The control section 80 determinesthe brightness of a photographic subject, for example, from a pixelsignal read before a pixel signal to be adjusted. In addition, theadjustment of the brightness of a through image may be performed bysetting a multiple for pixel addition in every field or in every frameaccording to the brightness of a photographic subject, with the exposureperiod being kept constant. When the above-described adjustment of thebrightness by the amplifier 724 and the above-described adjustment ofthe brightness by the pixel addition are utilized together, pixelsignals subjected to the pixel addition show that a photographic subjectis brighter than the actual brightness of the photographic subject.Therefore, determination of the brightness of a photographic subjectbased on pixel, signals requires consideration of a multiple for pixeladdition.

Next, the control section 80 stores pixel data output from the AFE 74 inthe RAM 100 in cooperation with the image processing controller 98. Itis noted herein that the vertical resolution of a frame represented bythe pixel data output from the AFE 74 is reduced in the verticaldirection by addition of signal charges. Therefore, the control section80 thins out pixels of the image data in the horizontal direction oradds up pixel values, which are continuous in the horizontal direction,according to the number of addition of the signal charges in thevertical direction, thereby reducing the vertical resolution of a framerepresented by the pixel data output from the AFE 74. As a result,distortion of a frame represented by the pixel data output from the AFE74 is corrected, and the resolution of the frame is reduced. By reducingthe amount of information of the pixel data as such, the amount ofprocessing to be performed on the image data afterwards can be reduced.

Next, the control section 80 generates frame data for one frame frompreviously read pixel data of a second field and currently read pixeldata (refer to FIG. 9) in cooperation with the color processing part102. Then, the control section 80 makes a frame represented by the framedata, which has been converted into frame data with a resolutioncorresponding to the screen size of the LCD 36, displayed on the LCD 16in cooperation with the resolution converting part 104, the imageprocessing controller 98 and the graphic controller 94. Meanwhile, thecurrently read pixel data is used for generation of the next frame data,along with pixel data to be read next time, as shown in FIG. 9. That is,in the DSC 1, a through image is displayed on the LCD 36 while the pixeldata read from the image sensor 72 is used for generation of frame datafor two continuous frames. In addition, generation of the pixel data ofthe field and generation of the frame data are performed in the sameperiod.

By using the pixel data read from the image sensor 72 for the generationof frame data for two continuous frames, the frame rate can be increasedas compared with a case (refer to FIG. 10 in which the pixel data isused for generation of frame data for one frame. In addition, when theimage sensor 72 is an image sensor which reads pixel signals of oneframe which is divided into a plurality of (three or more) fields, thepixel data read from the image sensor 72 may be used for generation offrame data for a plurality of continuous frames according to the numberof the divided fields. Further, the DSC 1 may be controlled so as to beable to be switched between a frame generating mode shown in FIG. 9 anda frame generating mode shown in FIG. 10.

Furthermore, the DSC 1 may read the first field and the second fieldalternately, and generate one frame of a monotone through image fromimage signals for one field whenever it reads one field. The frame of amonotone through image as a monotone moving image can be generated onthe basis of signal charges showing the density level of some channelsamong all the channels. For example, the frame of a monotone throughimage can be generated on the basis of signal charges showing thedensity level of a G channel of RGB channels. Therefore, the frame of acontinuous monotone through image can be generated from image signals ofa first field and image signals of a second field, which are continuous,on the basis of image signals of G channels commonly included in thefirst field and the second field. Here, the image signals of G channelsmeans image signals correlated to the signal charges showing the densitylevel of the G channels. As a result, since the number of times ofreading of fields required for generating one frame can be reduced, evenif a structure for a high-speed draft mode is not provided, the framerate of a through image can be increased. In addition, the DSC 1 mayread either a first field or a second field continuously, and may notneed to read the other field at all during display of a monotone throughimage. In this case, the DSC 1 generates one frame of a monotone throughimage from image signals for one field whenever it reads either thefirst field or the second field.

FIG. 11 is a flowchart showing the through image display processingwhich displays a monotone through image.

First, the control section 80 reads pixel signals of a first field(refer to Step S200). If pixel signals of a first field have been read,the control section 80 executes the processing of Step S202.

In Step S202, the control section 80 generates monotone frame data onthe basis of only pixel data of G channels of a first field.Specifically, for example, the control section 80 generates monotoneframe data for one field on the basis of only read pixel data of Gchannels in cooperation with the color processing part 102. Since theframe data is generated on the basis of only pixel signals of a firstfield, the number of times of field reading required for generatingframe data for one field can be reduced as compared with a case in whichthe frame data is generated on the basis of pixel signals of a pluralityof fields. Further, since the frame data is generated on the basis ofonly the pixel data of G channels, the processing amount of the pixeldata required for generating the frame data for one field can be reducedas compared with a case in which the frame data is generated on thebasis of the pixel data of G channels and pixel data of B channels. As aresult, the frame rate of a through image can be increased. In addition,the monotone frame data may be generated on the basis of the pixel dataof G channels of a first field and pixel data of B channels of a firstfield.

In Step S204, the control section 80 displays a monotone image for onefield on the LCD 36 on the basis of the frame data. Specifically, forexample, the control section 80 displays a frame represented by theframe data converted to have a resolution corresponding to the screensize of the LCD 36, in cooperation with the resolution converting part104, the image processing controller 98 and the graphic controller 94.

In Step S206, the control section 80 reads pixel signals of a secondfield similarly to the processing of Step S200.

In Step S208, the control section 80 generates frame data on the basisof the read pixel signals of G channels of the second field, similarlyto the processing of Step S202.

In Step S210, the control section 80 displays on the LCD 360 themonotone frame generated on the basis of the pixel signals of G channelsof the second field, similarly to the processing of Step S204.

By repeating the above-described processing of Step S200 to Step S210,the control section 80 displays a predetermined number of continuousframes of a monotone through image on the LCD 36.

In addition, generation of the pixel data of the field and generation ofthe frame data are performed in the same period.

Further, the DSC 1 may display continuous monotone frames on the LCD 36on the basis of pixel signals of G channels of a first field, which havebeen read continuously by repeating the processing of Step S200 to StepS204. Besides, the DSC 1 may display continuous monotone frames on theLCD 36 on the basis of pixel signals of G channels of a second field,which have been read continuously by repeating the processing of StepS206 to Step S210. By reading pixel signals of either the first field orthe second field, a time difference in exposure period betweencontinuous fields can be shortened, and signal charges can be read fromthe same photodiode 721 between the continuous fields. As a result, ahigh-definition, clear through image can be displayed on the LCD 36 ascompared with a through image based on the pixel signals of both offirst and second fields.

Second Embodiment

FIG. 12 is a schematic view of a DSC 300 according to a secondembodiment.

The DSC 300 is a so-called single lens reflex DSC including a mainmirror 302 and a sub-mirror 304. A central portion of the main mirror302 is composed of a half mirror. The sub-mirror 304 is disposed in thevicinity of the center of the main mirror 302 to reflect the lighttransmitted through the half mirror. Hereinafter, the central portion ofthe main mirror 302 is referred to as a half mirror part. The DSC 300includes the substantially same components as those of the DSC 1according to the first embodiment shown in FIG. 3.

When the main mirror 302 and the sub-mirror 304 takes a postureindicated by a dotted line in shown FIG. 12 (hereinafter referred to as“mirror-down state”), the light from a photographic subject which hasbeen transmitted through lenses 60 and 64 and incident on a portionother than the mirror half part of the main mirror 302 is reflected bythe main mirror 302. On the other hand, the light which has beentransmitted through the lenses 60 and 64 and incident on the half mirrorpart of the main mirror 302 is split into light which is reflected bythe surface of the main mirror and light which is transmitted throughthe half mirror part. The beam reflected by the main mirror 302 isguided to an eyepiece lens by a pentaprism (not shown) which is disposedabove the camera. In contrast, the light from a photographic subjectwhich has been transmitted through the half mirror part of the mainmirror 302 is guided from the main mirror 302 to an AF sensor module(not shown), which is disposed below the camera, by a portion of thesub-mirror 304 located on the side of the image sensor 72.

When the image sensor 302 takes a posture indicated by a solid line inFIG. 12 (hereinafter referred to as “mirror-up state”), the sub-mirror304 is folded until it takes a posture parallel to the main mirror 302so as to approach the main mirror 302. In the mirror-up state, the lightfrom a photographic subject is guided in the direction of the shuttercurtains 30 and 32, and incident on the image sensor 72 when the shutteris opened.

FIG. 13 is a flowchart showing the flow of processing in a photographingmode of the DSC 300. The processing shown in FIG. 13 is started when theDSC 300 transits to the photographing mode and is repeated until the DSC300 transits from the photographing mode to any mode other than thephotographing mode.

First, the control section 80 determines whether or not a preview buttonis pushed (refer to Step S300). Here, the preview button is an actuatorwhich allows selection of either a mode in which a subject isphotographed while being checked with a through image as a moving imagebeing displayed on the LCD 36 or a mode in which a subject isphotographed while being checked with an optical finder.

When the preview button is pushed, the control section 80 controls themain mirror 302 and the sub-mirror 304 so that they may take themirror-up state (refer to Step S302). Then, the control section 80executes the substantially same processing as that in Step S100 andS118. As a result, a photographer can photograph a subject whilechecking it with a through image as a moving image displayed on the LCD36.

On the other hand, when the preview button is not pushed, the controlsection 80 controls the main mirror 302 and the sub-mirror 304 so thatthey may take the mirror-down state (refer to Step S304). Then, sincethe light from a photographic subject is guided to an eyepiece lens asdescribed above, a photographer can check the photographic subject withan optical finder. Then, the control section 80 executes processing inStep S104.

1. A digital camera comprising: a lens; a first sensor that receiveslight through the lens; a shutoff member that performs a first shutoffof the light received by the first sensor through the lens and that endsthe first shutoff; a display that displays a moving image based on thelight received by the first sensor; a detector that detects a shutteroperation while the display is displaying the moving image; a secondsensor that receives light through the lens, the second sensor beingdifferent from the first sensor; an exposure amount determiner thatdetermines, in response to the detected shutter operation, an exposureamount based on the light received by the second sensor when the firstsensor does not receive light through the lens; and a still imagegenerator that generates a still image based on the light received bythe first sensor and the exposure amount determined by the exposureamount determiner.
 2. The digital camera according to claim 1, whereinthe exposure amount determiner determines the exposure amount after theshutoff member performs the first shutoff, the shutoff member ends thefirst shutoff after the exposure amount determiner determines theexposure amount, and the still image generator generates the still imageafter the shutoff member ends the first shutoff.
 3. The digital cameraaccording to claim 1, wherein the second sensor receives the light thatpasses through the lens and is diffused by a diffusing portion.
 4. Thedigital camera according to claim 3, wherein a surface of the diffusingportion is formed with satin.
 5. The digital camera according to claim3, wherein the diffusing portion is a shutter curtain.
 6. The digitalcamera according to claim 1, wherein the display displays the movingimage based on the light received by the first sensor with an electronicshutter.
 7. The digital camera according to claim 2, wherein the shutoffmember performs the first shutoff by closing a shutter curtain inresponse to the shutter operation, the shutoff member ends the firstshutoff by opening the shutter curtain after the exposure amountdeterminer determines the exposure amount, and the still image generatorgenerates the still image based on the light received by the firstsensor with the shutter curtain.
 8. The digital camera according toclaim 7, wherein after a period based on the exposure amount from a timewhen the shutoff member ends the first shutoff, the shutoff memberperforms a second shutoff of the light through the lens that is incidenton the first sensor.
 9. The digital camera according to claim 1, whereinthe display displays the moving image based on the light received by thefirst sensor after the still image generator generates the still image.10. The digital camera according to claim 1, wherein the first sensor isan area image sensor.
 11. A method of controlling a digital camera, themethod comprising: displaying a moving image based on light received bya first sensor, the light being received through the lens; detecting ashutter operation while displaying the moving image; determining, inresponse to the detected shutter operation, an exposure amount based onlight received by a second sensor that is not the first sensor, thelight being received by the second sensor, through the lens, when thefirst sensor does not receive light through the lens; and generating astill image based on the light received by the first sensor and theexposure amount being determined.
 12. The method according to claim 11,further comprising: performing a first shutoff of the light received bythe first sensor through the lens; and ending the first shutoff, whereinthe exposure amount is determined after the first shutoff is performed,the first shutoff is ended after the exposure amount is determined, andthe still image is generated after the first shutoff is ended.
 13. Themethod according to claim 11, wherein the second sensor receives thelight that passes through the lens and is diffused by a diffusingportion.
 14. The method according to claim 13, wherein a surface of thediffusing portion is formed with satin.
 15. The method according toclaim 13, wherein the diffusing portion is a shutter curtain.
 16. Themethod according to claim 11, wherein the moving image is displayedbased on the light received by the first sensor with an electronicshutter.
 17. The method according to claim 12, wherein the first shutoffis performed by closing a shutter curtain in response to the shutteroperation, the first shutoff is ended by opening the shutter curtainafter the exposure amount is determined, and the still image isgenerated based on the light received by the first sensor with theshutter curtain.
 18. The method according to claim 17, furthercomprising: after a period based on the exposure amount from a time whenthe first shutoff is ended, performing a second shutoff of the lightthrough the lens that is incident on the first sensor.
 19. The methodaccording to claim 11, further comprising: displaying a moving imagebased on the light received by the first sensor after the still image isgenerated.
 20. The method according to claim 11, wherein the firstsensor is an area image sensor.